Twin-wire web forming system with dewatering by centrifugal forces

ABSTRACT

A twin-wire web making system for use in forming multi-ply or single-ply webs wherein a web stock is discharged into a nip between opposed forming wire runs arranged to converge with one another over guide elements. In one embodiment a plurality of individual forming sequences are associated with a main forming wire for receiving successive plies and merging the same together at each sequence. In another embodiment a single forming sequence is associated with a pick-up felt for removal of the ply from the forming sequence. At each sequence a head box means discharges web stock between twin wires supported by spaced breast rolls defining the nip therebetween and the wires gradually converge into general parallelism over curved guides by wrapping a portion of their surfaces so as to centrifugally dewater the stock sandwiched between the wires. In one aspect of the invention, a stationary curved surface and a rotary cylinder are positioned on the same side of the wires to guide the wires into general parallelism. The stationary surface and the roll combine to define a bi-radii path of wire travel having a first radius of curvature larger than the second radius of curvature. The stationary surface is water impermeable or permeable and includes surfaces having a decreasing radius of curvature in the direction of wire travel. The rotary cylinder includes solid rolls, open rolls and suction rolls. The head box means includes structures containing a plurality of flexible trailing elements therein defining therebetween channels converging in the direction of the nip for producing a stream having a relatively low degree of turbulence and a relatively high degree of dispersion.

April 10, 1973 J. 0. PARKER ET 3,726,753

TWIN-WIRE WEB FORMING SYSTEM WITH DEWATERING BY CENTRTFUGAL FORCES FiledJuly 8, 1971 6 Sheets-Sheet 1 April 10, 1973 J. D. PARKER ETAL 3,726,753

TWIN'WIRE WEB FORMING SYSTEM WITH DEWATERING BY CENTRIFUGAL FORCES FiledJuly 8, 1971 6 Sheets-Sheet 2 April 10, 1973 J. D. PARKER ET 3,726,758

TWIN'WIRE WEB FORMING SYSTEM WITH DEWATERING BY CENTRIFUGAL FORCES FiledJuly 8, 1971 6 Sheets-Sheet 3 INVENTORS c/osgofi D. Parker flay/62 E62/5/67/500 'ddrmhr W W ATTORNEYS April 10, 1973 J, PARKER ET AL3,726,758

TWIN-WIRE WEB FORMING SYSTEM WITH DEWATERING BY CENTRIFUGAL FORCES FiledJuly 8, 1971 6 Sheets-Sheet 4 INVENTORS Jasi/w D. l /LQKE? 041/0 k.usmFsa/l/ QlTO/WEYS April 10, 1973 PARKER ET AL 3,726,758

TWIN-WIRE WEB FORMING SYSTEM WITH DEWATERING BY CENTRIFUGAL FORCES FiledJuly 8, 1971 6 Sheets-Sheet 5 2 f5- 7 INVEN'IORS jaszfi/ Q %eK e 04 W0 RGusmfs 04/ Wag a Apnl 10, 1973 J. D. PARKER ET AL 3,726,758

TWIN-WIRE WEB FORMING SYSTEM WITH DEWATERING BY CENTRIFUGAL FORCES FiledJuly 8, 1971 s Sheets-Sheet 6 United States Patent 3,726,758 TWIN-WIREWEB FORMING SYSTEM WITH DEWATERING BY CENTRIFUGAL FORCES Joseph 1).Parker, RR. 1, Southgate Road, Roscoe, Ill. 61073, and David R.Gustafson, 717 E. Franklin St., Rockton, Ill. 61072 Continuation-impartof abandoned applications Ser. No. 792,713, Jan. 21, 1969, and Ser. No.795,954, Feb. 3, 1969. This application July 8, 1971, Ser. No. 160,879

Int. Cl. D21f 1/36 US. Cl. 162299 23 Claims ABSTRACT OF THE DISCLOSURE Atwin-wire web making system for use in forming multi-ply or single-plywebs wherein a web stock is discharged into a nip between opposedforming wire runs arranged to converge with one another over guideelements. In one embodiment a plurality of individual forming sequencesare associated with a main forming wire for receiving successive pliesand merging the same together at each sequence. In another embodiment asingle forming sequence is associated with a pick-up felt for removal ofthe ply from the forming sequence. At each sequence a head box meansdischarges web stock between twin wires supported by spaced breast rollsdefining the nip therebetween and the wires gradually converge intogeneral parallelism over curved guides by wrapping a portion of theirsurfaces so as to centrifugally dewater the stock sandwiched between thewires. In one aspect of the invention, a stationary curved surface and arotary cylinder are positioned on the same side of the wires to guidethe wires into general parallelism. The stationary surface and the rollcombine to define a bi-radii path of wire travel having a first radiusof curvature larger than the second radius of curvature. The stationarysurface is water impermeable or permeable and includes surfaces having adecreasing radius of curvature in the direction of wire travel. Therotary cylinder includes solid rolls, open rolls and suction rolls. Thehead box means includes structures containing a plurality of flexibletrailing elements therein defining therebetween channels converging inthe direction of the nip for producing a stream having a relatively lowdegree of turbulence and a relatively high degree of dispersion.

CROSS-REFERENCE TO RELATED APPLICATIONS This is a continuation-in-partapplication of our copending U.S. Ser. Nos. 792,713, filed Jan. 21,1969, now abandoned, and Ser. No. 795,954, filed Feb. 3, 1969, nowabandoned.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesto fibrous web formation and more particularly to improved apparatus,systems and processes for forming fibrous webs from dilute aqueoussuspensions thereof.

Prior art In relatively recent years the art of web making, particularlypaper making, has undergone a number of significant advances in thefield of web formation using two opposed forming wire runs for webformation therebetween is contrasted to the heretofore more conventionalFourdrinier-type web making machines employing only a single formingwire. Although such twin wire forming machines have met with limitedcommercial success, these machines are still in the stage of beingimproved and various aspects of the operation thereof and the resultingquality of web may leave something to be desired, at least in certainspecific instances. For example, as the speed of the web making machineis increased, operational difii culties are often encountered inconnection with deposition of certain types of stock requiring ratherhigh dilution. The problems encountered are not limited to difficultiesin control of water movement (with resulting rolling and/or streaking)but include difficulties of web sensitivity in some speeds, prematurewear of various components, control of pressure applied on the new web,etc. Essentially, the instant invention provides a new and uniqueforming arrangement which accommodates higher machinery speeds as wellas improved quality web somade.

SUMMARY OF THE INVENTION The invention generally comprises a formingmachine and system including a head box means for providing aribbon-thin jet stream of web stock in a given direction (horizontal orvertical); two endless loop forming wires arranged to travel in thegiven direction so as to define a forming zone; a breast roll positionedWithin each of the looped wires to define a nip therebetween forreceiving the stock and curved guide elements positioned dOWIl-r streamof the breast rolls and within the loop of one of the wires to dewaterthe stock sandwiched between the wires.

In one embodiment, a main forming wire is guided through a plurality ofsequences, each sequence having an individual head 'box means and anauxiliary wire converging With the main wire over curved guide elementsso as to dewater the ply formed in that sequence and merge it withpreceding plies. In one specific form of this embodiment, the guideelements comprise a large diameter roll, which can be perforated orimperforated, positioned within the loop of the main wire and having itsouter surface partially wrapped by the traveling wires so as tocentrifugally dewater the stock between the wires. In another specificform of this embodiment, the guide elements comprise a stationary(perforated or unperforated) curved surface followed by a roll, bothpositioned within the loop of the main wire so as to define a continuousbi-radii curved path of travel having a first radius of curvature largerthan the second radius of curvature. A portion of the outer surfaces ofthe stationary surface and the roll is wrapped by the wires tocentrifugally dewater the sandwiched stock. The stationary surface has aconstant radius of curvature or a decreasing radius of curvature in thedirection of wire travel.

In another embodiment of the invention, a pair of forming wires areguided through an individual sequence having a head box means and meansgradually converging the wires into general parallelism over curvedguide elements to centrifugally dewater the stock between the wires. Aspecific form of the head box means includes walls converging toward theoutlet opening thereof and a plurality of flexible trailing elementswithin the head box slice chamber converging toward the opening forguiding aqueous stock as a ribbon-thin jet stream having a relativelylow degree of turbulence and a relatively high degree of dispersion intothe nip between the wires. A specific form of curved guide elementscomprise a stationary curved surface followed by a cylindrical roll,both positioned within the loop of one of the wires for guiding thewires through a change of travel direction to centrifugally dewater thestock between the wires. The stationary surface is so id or formed of aplurality of thin edges, the longitudinal contour of which define thedesired curves. The cylindrical roll is a relatively large diameterdewatering roll (open, suction, grooved, drilled, etc.). Couch andturning rolls are positioned within the forming run for separating theweb from one of the wires and guiding the web-carrying wire to a pick-upstation for transferring the web from the forming zone. In a specificarrangement, both wires wrap a portion of the couch roll to insure thatthe web remains in contact with the desired wire through a change ofwire travel direction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an essentially schematicelevational view showing a portion of a web forming machine composed ofa plurality of sequences embodying the instant invention;

FIG. 2 is an essentially schematic elevational somewhat enlarged view ofan individual sequence as the type shown in FIG. 1;

FIG. 3 is an essentially schematic elevational somewhat enlarged view ofanother embodiment of the individual sequence shown in FIG. 2;

FIG. 4 is an essentially schematic elevational view showing a portion ofa web forming machine somewhat similar to the type shown in FIG. 1 bututilizing the individual sequences shown in FIG. 3;

FIG. 5 is an essentially schematic elevational view illustrating afurther embodiment of the invention;

FIG. 6 is an essentially schematic elevational partial view of amodified form of the embodiment illustrated at FIG. 5;

FIG. 7 is an essentially schematic elevational partial view of yet afurther modified arrangement of the embodiment illustrated at FIG. 5;and

FIG. 8 is essentially a schematic elevational view illustrating yet afurther modification of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 generally indicates, asat 10 a portion of a forming section of a twin wire web forming machineembodying the instant invention and comprising from left to right, afirst sequence S1, a second sequence S2 and a portion of a thirdsequence designated as S3. In each of such sequences, S1, S2 and S3, anew ply of web is formed and is merged with the moist web ply orplurality of plies already on a main bottom forming wire 11. Suchpre-formed moist web ply or plies carried on the bottom main wire 11 isdesignated as P coming into the first sequence S1; P coming into thesecond sequence S2, and P coming into the third sequence S3.

It will be seen that the main bottom wire 11, which is a conventionalwoven metal fabric wire (although it might be a plastic wire or otherwire for special purposes) is guided, as by breast roll 11a so as topass over an initial large roll 12 (having a large curved surface) sothat the wire 11 wraps on substantially its upper downrunning quadrantQ12. In the first sequence S1, there is also a short looped upperauxiliary wire 13 having a plurality of guide and drive rolls 14, 15, 16and 17 mounting the same and driving the looped auxiliary wire 13 atsubstantially the speed at which the bottom main wire 11 is travelingthrough the sequence S1. It will be seen that there is a reach 13a ofthe auxiliary wire 13 which extends from a first top guide roll 14 to alower guide roll (which may be considered a third guide in the sequence,since the large roll 12 guides the top wire reach 13a as well as thebottom wire 11). The rolls 14 and 15 maintain the top wire reach 13aunder tension as it is wrapped into the configuration shown about thebottom wire 11 on the large roll 12. As is apparent, the deflected topwire reach 13a is free from restraining means in contact therewithopposite the bottom wire 11 throughout the quadrant Q12 of the largeroll 12. Skimming deflector means, indicated at 13b and 11b atapproximately the opcoming side of the guide roll 15 are shown onlyschematically, but such deflectors operate in close-running relation tothe wires 11 and 13, and are actually closely spaced therefrom so as toskim water carried along the back side of such wires without exertingexcessive pressure or hearing force on the traveling wires in the senseof a direction changing guiding type of contact (or pressure). Thesetype of skimmers can also be positioned along the q a rant Q12 as desied. pp p ia e ave all devices (not shown) may be positioned beneath eachsuch deflector and wipers 12a, 22a, etc. may be provided along theon-coming side of rolls 12, 22, etc.

The top guide roll 14 may thus be considered as a first guide in thesuccession of guides 14, 12, and 15 whereby the top wire 13 travelingover the first guide roll 14 and bottom wire 11 traveling over thesecond guide roll 12 at substantially the same speeds are brought intoinitially close spacing, as at J1 for receiving therebetween a jetstreamof web forming stock from a head box means, indicated essentiallyschematically at 18 and having a slice outlet at 18a. The slice outlet18a feeds a stock jet stream into a spacing J1 between the wires 11 and13. The wires 11 and 13 are brought through gradual convergence in a webforming zone (generally indicated by the dimension of F1) and intosubstantial parallelism with the ultimately formed fibrous web ply beingsubstantially merged with the original preformed web P carried into theforming zone F1 on the bottom wire 11. It will be appreciated that thewires 11 and 13 are in such substantial parallelism, that the tension onthe wires will cause a coutinned squeezing of moisture in the stock (ormoist web) therebetween. Additionally, the change of the direction ofwire travel over the surface of roll 12 causes centrifugal force to beexerted on the moisture in the stock and to be thrown through the wiresand away from a forming zone. The wires also pass the skimmingdeflectors 13b and 11b and then turn comparatively abruptly about thethird guide, i.e. the suction roll 15, so as to wrap the suction area15a of such suction roll in order to effect yet further dewatering. Inthis instance, the dewatering is carried out in part by water drawn inand held in a suction area and also by water thrown through and from themain Wire 11 as it turns about roll 15. The wires 13 and 11 thencontinue in such substantial parallelism with the newly formed moist WebP therebetween until they reach the guide roll 16 for separating the topauxiliary wire 13 from the web and a suction roll 19 having a suctionarea 19a engaging the underside of the main bottom wire 11 formaintaining the newly formed web P thereon as it passes to the nextsequence S2.

It will be appreciated that the elements shown in the second sequence S2which correspond to those already described in connection with the firstsequence S1 are designated by the same reference numerals in the twentyseries. Thus, the initial three successive guides are shown as the toproll 24, the large roll 22 and the lower suction roll 25. A fresh diluteaqueous suspension of entangled co-moving web fibers will exit from theslice 28a as a high speed substantially unidirectional ribbon-thinjetstream into the spacing J2 that is effected initially by the guides24 and 22 serving to bring the top wire 23 into initially close spacingwith the bottom wire 11 at the large end J2 of the region of convergencewhich defines the forming zone F2 for the new ply that is being formedin sequence S2 and ultimately merged into the composite web product Pleaving the sequence S2.

As indicated in FIG. 1, the arrangement in each of the sequences S1, S2,S3, etc. are extremely simple and alford a considerable amount ofversatility in operation. Also, such arrangements are found to give goodwire life to the typical short wire loops 13, 23, etc. in that suchshort wire loops 13 are carried entirely by co-moving guide elements inthe form of rolls 14, 16 and 17 and the suction roll 15, arranged toavoid excessive reverse bending. Likewise, the main bottom forming wire11 is mounted only in co-moving elements which are indicated as thelarge rolls 12, 22, etc. and the smaller rolls 19, 29, etc. The bottomwire 11 will actually have a lower return run, and the view in FIG. 1shows what constitutes the upper run of the wire 11, but it isfunctionally the bottom wire in the arrangement hereshown and it is sodesignated for convenient reference.

In spite of the apparent simplicity of the overall arr g ment shown inFIG. 1, certain functional and very significant operational advantagesare afforded in this arrangement. It has been indicated that in allexcept an original web forming sequence in the overall system designated10, there will be a preformed moist web ply traveling on the bottom wire11. This being the case, the dewatering at the forming zone indicated inFIG. 1 at F1, F2, F3, etc. involved forming zones wherein dewateringwill take place primarily through the top wire runs 13a, 23a, etc.although some dewatering will also take place through the lower mainwire. This affords a substantial convenience in cost and maintenance byallowing the use of a plain large roll for the rolls 12, 22, 32, etc. Ofcourse, perforated or imperforated (i.e. open) rolls (as more clearlydescribed hereinafter) can also be used, especially where an initial webply is first applied to the bottom wire 11, but this would not beabsolutely necessary either and the very first sequence could operatesubstantially as has been described already in connection with thesequence S1, except there would be no initial ply P carried on thebottom wire 11. The bottom wire 11, however, should wrap the roll 12 toobtain the desired centrifugal dewatering of the stock in the area ofthe forming zone F1.

Referring now to FIG. 2, certain of the more significant advantages ofthe individual sequences will be described; and the sequence in FIG. 2will be designated for a convenient reference as S4 and all of thevarious elements of FIG. 2 which correspond to elements previouslydescribed will be designated by the same reference numeral in theseries. Thus, the inlet 48 shown only partially, has a slice from whicha substantially unidirectional ribbon-thin jet-stream exit in apredetermined direction at a predetermined linear speed (signifiedmerely by the arrows and dashed lines). Also, this sequence S4 isprovided with spaced successive first 44, second 42 and third guides (orguide rollers) and opposed top 43 and bottom 11 forming wires or beltstraveling at substantially the jet stream speed over the first guideroll 44 and the second guide roll 42, respectively and through initiallyclose spacing at J4 for receiving therebetween the jet-stream andsubstantially immediately thereafter through gradual convergence in aweb forming zone F4 and into general parallelism with the fibrousforming web therebetween, in which parallelism the wire runs 11 and 43travel downstream together over the third roll guide 45 in a manneralready described in connection with the previously discussed sequence.

In the embodiment of FIG. 2, it will be seen that the skimming deflector43b for the inside of the top wire 43 is shown in closely spacedclose-running relation to the wire 43 and is also shown as part of alarger save-all assembly 430. A skimming deflector 11b is likewise shownin a very closely spaced close-running relation to the wire 11 and is apart of a save-all assembly 42b, which includes a wiper 42a at theup-running side of the large roll 42.

There are several advantages which may be considered in connection withthe specific form of the invention illustrated at FIG. 2. For example,although adjustability as to the extent of wrap by the top wire 43 andalso as to the tension of the top wire reach 43a between the guide 44and 45 may be adjusted by a number of different ways, such adjustabilityas indicated only schematically by the double-headed arrows designated44a for the top roll 44 hereshown. It has already been pointed out thata substantial amount of wrap of both wires in the upper down-runningquadrant Q42 for the large roll 42 is important. In the light of theavailable control of tension on the wire reach 43a, it will beappreciated that, at any given operating speeds and conditions at thestock jet slice 48a, the tension of the reach 43a affords a selfadjusting and steady pressure forming zone wherein control of theseessential conditions is readily achieved.

Under such conditions as the self-adjusting of the pressure within theforming zone F4 which is here afforded,

it may be appreciated that the overall length or peripheral dimensionavailable for use as the forming zone may extend from approximately thelocation designated A near the top of the roll 42 to the locationdesignated B near the end of the quadrant Q42 (at which location thewires 11, 43 are actually separated from the surface of the roll 42 bythe guide roll 45, which can also be adjustably positioned so as tochange to some extent the point of separation of the wires from thesurface of the roll 42). The present arrangement, the roll 42 has apreferred diameter of four feet and the actual forming zone F4 has aperipheral dimension 11, preferably equal to about As a practicalmatter, however, the peripheral dimension of the forming zone may rangefrom about 10 to as much as about 180 (and preferably ranges from about60 to about Dewatering of the jet-stream at the relatively largediameter arcuate surface A-B of the roll 42 is effected by thecentrifugal force resulting from the arcuate travel of the wirescarrying the newly forming web therebetween around the portion A-B ofthe roll 42 and by the pressure caused by the wire tensions actingagainst the web expressing water therefrom.

Still an additional feature of significance in connection with thisarrangement resides in the fact that there will be a hydraulic head It,substantially equal to the overall vertical dimension from A to B, whichaffords development of higher drainage pressures within the forming zoneF4, without a sacrifice of velocity head of the stock between the Wires.In this respect, the size in alignment of the forming zone F4 willreflect the development of pressure resulting from this hydraulic head hindependently of the machine speed which affords a distinct advantage inadditional control of the operation. In other words, the head h will beconstant irrespective of the speed of the machine and the extent of thecentrifugal force.

Another at least partially independent aspect of control of the drainagepressure is afforded via the alignment in speed of the jet-streamfeeding into the initial close spacing J4 between the wires 11 and 43.It will be appreciated that the traveling speeds of the wires 11 and 43are controlled so as to be substantially equal; and such speed islikewise substantially equal to that of the stock jet-stream, but notnecessarily absolutely identical thereto. In other words, as shown bythe slight apparent expansion of the stock jet as at S14 just beyond thetop of roll 42, the stock jets may be adjusted so that at this specificregion S14, a certain amount of the jet-stream speed is lost andconverted to pressure normal to the wires 11 and 43, i.e., an initialdrainage pressure. In this way, the inlet to the forming zone isadequately sealed (i.e. in the general region of J4) and effectivedrainage and incipient web formation is thus initiated rapidly.

Also, the general curvature of the wires 11 and 43, and primarily of thebottom drainage wire 11, is a curvature that is generally consistentwith the trajectory of the jet, at least to the extent that by selectiveadjusting of the alignment of the jet (by an adjustable means, indicatedschematically at 48b by the two-headed arrow) it is possible toco-relate the jet trajectory much more closely with the generalcurvature of the wire in this arrange- I ment, and in so doing, effectthe type of sealing of the jet at the nip region S14 in the mannerindicated schematically herein, which essentially involves thecontinuous maintenance of a slight expansion of the stock stream toslightly greater thickness than the jet-stream iself at this closelyspaced nip of the converging wires. It will be appreciated that themaintenance of the slight stock expansion at the region S14 is acondition that can be stabilized during operation and the expansion thusmaintained continuously so as to afford a pressure within the stock bodyduring the initial web formation. Impingement of the stock into the areaS14 avoids any significant disturbance of the jet stream, such as may becaused by the partial pressure experienced on the off-running side 7 ofsolid surfaces in phenomenon commonly known as pumping.

As indicated previously, in the case of the formation of an initial ply,an open roll (perforated or imperforated) free from the wrap of theforming wires and facing down in the position 42 would have itsadvantages because of the convenience of gravity assisting dewatering ofthe roll into which water had been forced during the forming period; butin the case subsequent formation applies, the economic advantages of asolid roll are available and the problem of drainage control is quitesimple and easily handled. There is no need for deflectors or otherdevices causing a pressing of the wires together, since the wires 11 and43 are pressed together while co-moving and while engaging a co-movingguide in the form of roll 45. The skimmers 43b and 11b simply serve toavoid any tendency to over-load a connection with the drainage at theimmediate location of the roll 45 which will, of course, press the wirestogether against the newly formed moist web sandwiched therebetween andeffect additional dewatering thereof.

In the embodiment described in FIG. 2, it will be appreciated that thehydraulic head h is approximately one foot or slightly more indiamension, but advantage resulting from the use of such hydraulic headin dimensional ranges from one inch to perhaps six feet are effected(the preferred dimensional range for the hydraulic head ranges fromabout one half to two feet).

Additionally, it will be appreciated that the arrangement of FIG. 1permits formation of an initial ply at a first sequence S1 (where Pwould have no meaning or would indicate that no ply was already on theoncoming wire 11); and subsequent sequences could then apply successiveplies as disclosed. -In so forming the initial ply the forming zone isreadily adjustable with regard to its peripheral dimension. Below thefirst quadrant Q12 (i.e. for as much as the next 90 of the righthandlower down-running quadrant) the second wire 13 will be used to controlstock flow while web formation is still in progress to the extent thatthere may be free stock on the surface of the web undergoing formation.The hydraulic head would, in the last mentioned situation, extend fromthe point of initial deposition of the jetstream J1 onto the roll 12downwardly to substantially the lower end of the actual forming zone, sothat the jet-stream may continue in this path without substantialvelocity loss but with continuous internal pressure increase via theincrease hydraulic head.

An important advantage of the invention resides in the use of arelatively large diameter roll 12 having a peripheral contour in theuper quadrant Q12 such that the configuration of the lower wire 11supported thereby may closely approximate the natural configuration(i.e. trajectory) of the stock jet-stream J1 exiting from the inlet atthe selected thickness and linear speed (and as it is effected bygravity, etc.). The more closely the traveling wire 11 may be co-relatedto this configuration (i.e. jet trajectory) and to the speed of thejet-stream, the less necessary the top Wire 13 becomes (at least at theearly stages of web formation); but conversely the advantages affordedby the top wire 13 varies from helping to contain the jet-stream, toaffording still more fine and delicate control as to the jet-streamspeed, as by exeluding resistance of ambient atmosphere, and by thepressure which wire 13 can exert in complementing the hydraulic headeffect. The optimum control under the foregoing conditions is obtainedin the upper quadrant Q12, and by using this region as the main formingzone (so that its configuration as defined by both wires 11 and 13 mostclosely represent the jet trajectory), the additional advantage ofseparating both wires 11 and 13 from the periphery of the roll 12 atleast substantially by the end of the upper quadrant Q12 permits gravitydewatering of the unwrapped roll 12 under the most favorable conditions.In conforming both wires to the trajectory inherent in the jet, the roll12 is selected for optimum size (i.e. diameter) and optimum positionbelow the inlet 18a. The jet-stream velocity and thickness are likewiseco-related to conform as closely as possible to those required forproducing the trajectory best suited for the roll size and position,which will determine primarily the lower Wire 11 configuration. Theconfiguration of the upper wire 13 is determined by roll 12 and the wire11 positions and configurations, plus the tension effect of rolls 14 and15 on the wire 13 as urged against the jet-stream on the wire 11 which,of course, resists the wire 13 (deflecting it with the initial force ofthe stock stream).

Referring now to FIG. 3, certain of the most significant advantages ofanother embodiment of the individual sequences discussed in relation toFIG. 2 will be described; and the sequence in FIG. 3 will be designatedfor convenient reference as S5 and all of the various elements in FIG. 3which correspond to elements previously described will be designated bythe same reference numeral in the 50 series. Thus, the inlet 58, shownonly partially, has a slice 58a from which exits a substantiallyunidirectional ribbon-thin jet-stream in a given direction and at apredetermined linear speed. Also, this sequence S5 is provided withspace successive first 54, second 71, and 52, and third 55 guide membersand opposed top 53 and bottom 11 forming wires traveling atsubstantially the jet-stream speed over the first guide 54 and secondguide 71 and 52 respectively and through initially close spacing at J5for receiving therebetween the jet-stream and thereafter through gradualconvergence in a web forming zone F5 and into general parallelism withthe fibrous forming web therebetween, in which parallelism the wire runs11 and 53 travel downstream together over third guide 55 in the mannerdescribed in the previously discussed sequences. Of course, as will beappreciated, if desired, a single ply can be formed and removed from thesequence S5 by an appropriately positioned pick-up felt (not shown)downstream of the roll 55.

The sequence illustrated at FIG. 3 is especially useful where there is atendency for the jet-stream of stock to be trapped between theconverging wires 53 and 11 and be squeezed outwardly at the sides of themachine so as to spew. To reduce this tendency, the arrangementillustrated in FIG. 3 is utilized to reduce the rate of convergence ofthe wires as gradually as possible. In other words, the effectivediameter of the roll 52 is increased by the utilization of a stationarycurved surface for plate 71 located between the roll 52 (at theon-coming side thereof) and the head box outlet 58a so as to extend intothe nip or area of convergence formed between the wires 53 and 11 asthey meet on the periphery of roll 52. The bottom wire 11 is trainedover the arcuate stationary surface of the plate or shoe 71 as thejet-stream is deposited thereon from the head box nozzle 58a. In thismanner, the rate of convergence between the two wires is more gradualand consequently dewatering pressure on the jet-stream is applied in amore uniformly increasing manner. It will thus be appreciated that thecombination (or cooperation) of the plate or shoe 71 with a largediameter roll 52 provides a relatively large arcuate surface which morereadily assumes the trajectory of the jet-stream and allows for a moreuniform application of pressure to the jet-stream as it is depositedbetween the wires. Thus, in effect, the portions of the curvedstationary surface Y71 and the cylindrical roll 52 cooperates to providea single wire guide having a relatively large diameter arcuate surfacewhereby the initial curvature of the nip between the converging wires ismuch less than would otherwise be available. Thus, the roll 52 ispositioned immediately adjacent the off-running side of the shoe 71 andthe actual spacing between elements 71 and 52 is not critical. Only thecooperation of these elements to define a gradually converging path ofwire travel is essential so that other dewatering elements, notinterfering with this cooperation, can be positioned therebetween. Thecurved plate 71 eifectively increases the diameter of the forming rollsin a relatively simple manner and, since the rate of curvature of thisplate is relatively small, very little, if any, normal (i.e.perpendicular) loading of the wires occurs at such plate. The curvatureis such that as the wires are nipped together, they experience everyincreasing curvature up to that of the roll and thereafter experience arelatively constant curvature substantially as shown to producecentrifugal forces on the newly deposited web between such wires fordewatering thereof. The curved plate 71 is machined or manufactured forhaving a desired radius of curvature, which may be constant (as shown atFIG. 4 at plate 171) or have a decreasing radius of curvature in thedirection of wire travel (as shown at plate 71). Additionally, thesurface of plate 71 may be perforated or imperforated.

The wires 11 and 53 gradually converge until they actually attaingeneral parallelism, as by contacting the rotating peripheral surface ofroll 52. The term general parallelism or substantial parallelism asutilized herein is defined for the purposes of the instant discussion asdescribing a dynamic concept of two wires spaced apart by a moist webcontinuously moving closer to each other as water is removed from such aweb. The Wires continue traveling in such substantial parallelismthrough the forming zone F5 and down to third guide 55. Guide 55 is hereshown as a suction roll having a suction gland 55a, and in oneembodiment, an adjustment means 55b is mounted thereon to allowadjustment of the amount of wire wrap on the roll 52. A similaradjustment means 54a is also provided on roll 54 to likewise control theamount of wrap of the wires over the guide surfaces. As the wiresdiverge from the surface of roll 52 they contact skimming devices 5312and 11b along the respective inner surfaces to remove water therefrom.These skimming devices 53b and 11b maybe incorporated with conventionalsave-all devices 53c and 52b to prevent the removed water fromre-contacting the forming web. Save-all device 52b may also be providedwith a wiping device 42a for removing adherent water droplets and thelike from the peripheral on-corning surface of roll 52 prior to itscontact with the main forming wire 11.

FIG. 4 indicates generally, at 100, a portion of a forming system of atwin-wire web forming machine embodying the instant invention thesequence'described in FIG. 3. It will be noted that generally thevarious elements are quite similar to that illustrated in FIG. 1, exceptthat various elements are designated in the 100 series and that onlysuccessive sequences are shown. From left to right a first sequence S11,a second sequence S12 (only a portion of which is shown) are designatedand it will be understood that additional sequences may be utilized asdesired, and that these sequential sequences cooperate to produce amulti-ply web of a desired thickness. In each such sequence S11, S12,etc. a new ply of web is formed and merged with a moist web ply or aplurality of plies already on the main bottom wire 111. A pre-formedmoist web ply or plies carried on the bottom main wire 111 designated Pcoming into the first sequence S11; P coming into the second sequenceS12, etc. It will be seen that the main bottom wire 111 passes over astationary curve (water-impermeable) shoe or plate 171 having arelatively constant radius of curvature and immediately thereafter overa relatively large diameter rotating roll 112, to wrap roll 112 onsubstantially its upper down-running quadrant Q112. In the firstsequence S11, there is a short loop upper or auxiliary wire 113 having aplurality of guide and drive rolls 114, 115, 116 and 117 mounting thesame and driving the looped wire 113 at substantially the speed at whichthe bottom wire 111 is traveling through the sequence S11. The reach113a of the top wire 113 extends from the first upper guide roll 114 toa lower guide roll 115. The guide rolls 114 and 115 maintain the topwire reach 113a yieldably under tension as it is wrapped in theconfiguration shown about the bottom wire 111 on the large roll 112.

Also the deflected top wire reach 1130 is free from restraining meansopposing the bottom wire 11 throughout its travel of the quadrant Q12 ofthe large roll 112. However, it will be appreciated that dewateringelements, such as skimming deflectors and the like, could be positionedin close running contact with the wire 113 throughout its travel of thequadrant Q12 for removal of any expressed water. Various skimmingdevices and foil means, as indicated at 113b and 1111) are positioned inclose-running relation with opposed surfaces of the wires to skim watertherefrom without exerting excessive pressure on such Wires and may beintegrally connected with conventional save-all devices 1521). Ofcourse, wiping means, such as schematically indicated at 112a, can beconnected with the various rolls for cleaning the oncoming surfaces ofsuch rolls.

The gradual convergence of the bottom wire 111 with the upper wire 113over the relatively large radius guide surface defined by the stationaryshoe 171 and the roll 112 prevents spewing of the jet-stream frombetween the Wires and serves to define a continuous bi-radii path oftravel having a first radius of curvature substantially larger than thesecond radius of curvature. Apparently, spewing of stock from betweenthe wires is limited or at least dependent upon the rate of pressureincrease in the nip. Thus, when the pressure between the wires increasesto a sufficiently high value, which may be only a few inches of water,the stock between the wires becomes thickened through drainage and suchstock will be forced out between the wires in a spewing manner.Decreasing of the initial curvature of the nip between such wires allowsthe jet stream of stock to be subjected to generally uniformlyincreasing gradual pressure, materially aiding in the dewatering thereofand preventing spewing. The stationary arcuate plate or shoe, designated171 in the sequence S11 and 171a in the sequence S12, increases theeffective diameter of the roll 112 and 122 respectively and therebyallows a more gradual consolidation of the jet-stream between the twowires as they approach each other and the roll surface.

A method embodiment of the invention based on the foregoing systemcomprises introducing a stream of web stock between co-moving andconverging opposed wires, guiding the superimposed wires with the stocksandwiched therebetween around a portion of a periphery of a wire guidehaving a large curved surface whereby the stock is dewatered through oneor both wires as the combined action of centrifugal force andconsidation of the stock by the wire tension acts to dewater the stock.The newly forming web is carried onwardly for further dewatering overadditional guides before the wires are separated to expose a web. Thecurved wire guide may comprise a large diameter roll or a combination ofa stationary arcuate plate positioned on the on-coming side (preferablywithout the intervention of any elements which cause any meaningfulchange in the direction of wire travel) of a large diameter perforatedor imperforated roll whereby the effected diameter of such a roll ismaterially increased.

The apparatus embodiment based on the systems of the invention describedcomprises first and second continuous forming Wires, which arepreferably foraminous, arranged to converge and provide an entrance nipfor the reception of stock, a curved guiding element adjacent theentrance nip, means for supporting the wires within their respectiveloops and moving them into said entrance nip, with the wires beingarranged to travel over the guide elements downstream of the entrancenip while having stocks thercbetween around a part of the periphery ofthe guide elements so as to centrifugally dewater the stock between suchwires. In one specific form, the guide element c0111- prises a portionof the surface of a large diameter perforated or imperforated roll andin another specific form the guide element comprises such a rollpreceded by a curved stationary perforated or imperforated surfacepositioned to define a continuous bi-radii path of travel with the roll.

The remainder of the discussion will now be devoted to the embodimentsof the invention forming a single web ply, however, it will beunderstood that this is not a limitation but merely further exemplaryembodiments of the invention.

FIG. illustrates a forming section 210 of a web forming system. The headbox means 211 is connected to a slice chamber 211a, having a pluralityof simultaneously converging sidewalls 211b, 21111 and a slice outlet211e. The head box provides a supply of web stock to the slice chamber211a. The slice outlet 211e is positioned at the upstream end of thesystem 210 so as to provide a jetstream of stock in a given direction.Upper sidewall 211b' is provided with an adjustable lip 2110 forselectively adjusting the size of the slice opening 211e. A poweradjustment means PA is positioned above movable lip 211a for selectiveadjustment as indicated. A plurality of flexible trailing elements 212are suitably mounted within a slice chamber 211a. It will be noted thatthe trailing members 212 are arranged to define plurality of convergingchannels 213 therebetween directing the passage of web stocktherethrough toward the opening 2112. Thus, an essentially symmetricalslice chamber 211a is attained. The slice chamber 211a is exceptionallywell suited for producing a dilute aqueous suspension of entangledcomoving fibers having a relatively low degree of turbulence and arelatively high degree of dispersion exiting downstream-Wise from theslice opening 211a as a high-speed substantially unidirectionalribbon-thin jet-stream. Additional details of such a preferred slicechamber are disclosed and claimed in copending Hill et al. application,U.S. Ser. No. 698,633, now Pat. No. 3,607,625, which disclosure isincorporated herein by reference. It will be appreciated that otherslice chambers produced in the desired characteristics within thejet-stream may also be utilized.

A pair of breast rolls 215 and 216 (open or solid) are mounted along acommon plane in working relation with the slice chamber 211a. The breastrolls 215 and 216 are spaced apart a distance somewhat greater than thetransverse or ribbon-thinness dimension of the jet-stream so as todefine a nip or gap G therebetween. In this regard, it will beappreciated that rolls 215 and 216 need not have their axes exactlyaligned along either a horizontal or vertical plane and that one or theother of such rolls may be aligned so as to have its axes along thegenerally parallel but difierent vertical or horizontal planes. The spacing between the surfaces of such rolls actually defines the gap G andnot the roll axial alignment. The jet-stream exits from the opening 211eof the slice chamber 211a into the gap G in a pressure-creatingrelationship. The relationship is such that substantially no floodingoccurs at the gap G and the speed of the jet-stream is substantiallyconverted into pressure. It will be noted that in the arrangementsshown, the jet-stream is orientated upwardly. A first forming wire Fwraps the first breast roll 215 and travels therewith through the gap G,while the second forming wire F wraps the second breast roll 216 andlikewise travels through the gap G. The forming wires are respectivelytrained over a plurality of wire guides 218, 219, 221 and thenrespectively over guides 223, 215a, 224 and 216a to define a first andsecond wire run. For sake of convenience, the first wire and first wirerun will be referred to by reference designation F while the second wireand second wire run will be referred to by the reference designation FThese forming wires may be composed of bronze, steel, copper, plastic oreven fabric strands woven in an open mesh to define endless loops. Theforming wires may also be formed of a plurality of different materialscombined to yield certain specific characteristics, i.e. wear, stretch,weight, strength, dewatering characteristics, etc.

While it is previously indicated that the jet-stream of stock impingesinto the gap G between the rolls 215 and 216, it will be noted that infact, the jet stream impinges 12 on the surfaces of the forming wires Fand F as they travel over the rolls 215 and 216 and that the streamcontacts one of the wires, i.e. F before the other. Dewatering occurs atthe off-running side of the roll 21S and 216 by essentially a drainagephenomena without any pumping by the rolls. Pumping is generally definedas the action of a diverging solid surface acting on a moving stream (ofstock or newly forming web) by creation of at least partial vacuum atthe off-running side of such surface which tends to pump or pull waterfrom the stream and thereby disrupt it. During early stages of webformation, pumping is detrimental to proper distribution and thus is tobe avoided. At this early stage of the forming section, substantiallylittle, if any mechanical pressure is exerted on the stock. This easypressure allows a substantial portion of the water to be drained fromthe forming zone without the application of disruptive pressures, whichmay cause shearing or like effect disturbing the proper formation of aweb. The dewatering, as indicated at a first area A and at a second areaA is in substantially opposing directions so that simultaneous drainage,without pumping, takes place along both surfaces of the newly formingweb allowing proper distribution of the fibers within the Web. Theforming wires F and F continue to travel convergingly together intogeneral parallelism over dewatering guides positioned downstream of thegap G.

The term general parallelism as used herein is to be understood toinclude the dynamic or changing re lation of the wires toward oneanother as caused by the slight spacing or separation of such wires bythe sandwiched web or web stock therebetween and allow the slightmovement of the respective wires toward one another as water is removedfrom such sandwiched web. As will be appreciated, as the stock(sometimes referred to as the jet-stream) is dewatered, the wire tensionurges the wires closer toward one another due this smaller quantity ofmatter between such wires. Thus, the tensioning of the respective wireruns materially aids in properly dewatering the forming web.

The first curved guide surface encountered by the converging wires iswire guide 218 which comprises an essentially elongated, smooth,stationary generally convexly curved surface urging the wire F intogeneral parallelism with wire F It is to be noted that wire F is freefrom restraining means throughout its travel through the forming zones,i.e. it is not associated with any elements which would prevent waterfrom being expressed through its inner surface. In the embodiment hereillustrated, wire guide 218 is shown as being waterimpermeable, however,as will be discussed in relation to FIG. 7, it may also bewater-permeable. The generally elongated curvature of the wire guide 218allows the application of easy pressure (a gradual build-up of pressurebetween the forming wires) and avoids spreading or spewing large volumesof Water from between the wires causing flow disturbances due torelatively abrupt and/ or intensified pressure changes between suchwires. In addition, the general curvature of the wire guide 218 causeslittle if any normal loading of the traveling Wires against the wireguide 218. The greatest loading actually occurs at the off-running sideof the wire guide 218. Substantially little, if any wear takes placealong the surface of the wire guide 21.8 since a minimal amount offrictional contact between the moving wires and the stationary surfacetakes place. It will be noted that the forming wires F and F do not comeinto actual parallelism with one another until some point 218a wellbeyond the lead edge of Wire guide 218. During the gradual convergenceof the wires into general parallelism additional pressure is exertedupon the newly forming web to express additional Water therefrom. Thewater is thrown through and away from the exposed side of the formingwire F which is, of course, free from contact with any restraining meansas defined hereinbefore. The expressed water is collected in a save-all13 device 217 having a conduit C directing the expressed white waterback to the head box or other desired location. A conventional doctormeans 21Gb is trained on the off-running side of the roll 216 to removeany adherent water particles, etc. from the surface of roll 216 anddirect the same into the save-all device 217. Of course, similar doctormeans can be associated with the various other rolls shown.

A large diameter foraminous roll 219 is positioned downstream of thethird wire guide 218, and preferably immediately downstream of theoff-running side of the wire guide 218 so as to define therewith acontinuous bi-radii path of travel having a first radius of curvaturesubstantially larger than the second radius of curvature. As indicatedin conjunction with the discussion relating to the earlier embodiments,the stationary surface 218 and the roll 219 are so positioned in respectto one another as to define a continuous bi-radii path of travel,however other dewatering elements positioned between the curvedstationary surface and the roll which do not alter the continuousbi-radii path of travel are within the scope of the invention. The roll219 is here shown as being an open breast roll having a perforatedsurface 219a for receiving water expressed through the bottom wire F Aswill be appreciated, dewatering takes place on both sides of thesandwich arrangement, i.e. water tends to be thrown away from the wire Fby virtue of centrifugal forces and into the openings of roll 219 byvirtue of positive pressure between the wires.

The relatively large radius of curvature of wire guide 218 substantiallyprevents normal or perpendicular loading of the wires F and F againstthe surface of the wire guide 218. In this manner, relatively littleWear takes place between the traveling wires and the stationary wireguide surface 218. The greatest amount a wire loading occurs when thewires come in contact with the rotary surface of the roll 219. However,since the surface of the roll 219 is rotating, substantially littlefrictional force is developed between the surface of the roll and thetraveling wire so that no detrimental effects are encountered by thevirtue of the increase loading on the wires. In the arrangement shown,the roll 219 guides the traveling wires through a substantial curve, offor example about 90, in a direction away from the jet-stream directionat the slice opening 2112 or the gap G. The rate of turn through whichthe traveling wires are forced by the curved guide elements issufiicient to cause dewatering to occur by driving water through andaway from the exposed side of forming wire F As will be noted, theexposed or inner peripheral side of the forming wire F is free from anyrestraining means (as defined hereinbefore) throughout the entireforming zone. The roll 219 is driven by virtue of tension in thetraveling wire runs, which are driven at substantially the jet-streamspeeds so that there is substantially no relative movement between thetraveling wire runs and the supporting surface of wire guide 219.Further, at this stage of the forming zone, the newly forming web willstill be in a relatively fluid stage and the relative shifting betweenthe wires as they travel over the rather abrupt curvature of roll 219does not cause shearing or the like to take place within the newlyforming web. In other words, some relative movement between two wirescan be tolerated at this relatively early stage of the forming zone.

A laterally continuous dewatering means 21% is trained on the exposedinner side of forming wire F at the off-running side of the roll 219.Dewatering means 21% is placed in extremely close working relationshipwith the traveling wire run to skim off water that may be adhering tothe backside of the forming wire run. The dewatering means 21% thusengages and removes water that is adhering to the backside of the wirerun but does not cause any wire-directional change and there is little,if any, frictional engagement between the traveling wires and thedewatering means 21%. Thus, it will be appreciated that stationarydewatering means 2191: would not constitute a restraining means forWater being expressed through the backside of a wire. As shown, thedewatering means 21% removes the water from the wire F and throws itinto a save-all device 217 having an appropriate conduit C passing theexpressed water to a desired location. As indicated hereinbefore, theabrupt change of direction that the traveling wires are forced toundergo by virtue of a curvature of the surface of roll 219 causes thewater within the newly forming web to be thrown through and away fromthe exposed side of the forming wires. The wire tension continuouslyurges the wires toward one another so as to drive water from thesandwiched web, while the abruptly curved surface provides momentum tothe expressed water along the surfaces of the wires away from the web.In other words, centrifugal forces and gravity are combined to effect asubstantial amount of dewatering at the area of curvature of the variousguides.

The two wire runs continue in general parallelism over an additionalwire guide 221. The wire guide 221 presents a water-removing surface,here shown as a plurality of stationary suction boxes acting against onesurface of the sandwich arrangement (wire-web-wire). It will be notedthat during the initial travel of the sandwich arrangement over thewater-removing surface of the wire guide 221, the inner peripheralsurface of forming wire F is free from contact with any detrimentalrestraining means while the inner peripheral surface of forming wire Fis in contact with the suction boxes of the wire guide 221 for removalof water therethrough. During the latter portion of travel of thesandwich arrangement over the suction boxes, the reverse occurs, i.e.suction box 221a contacts the inner peripheral surface of forming wire Fwhile the inner peripheral surface of wire F is free from contact withrestraining means. The newly formed web tends to adhere along thesurface of Wire F and continues to travel therewith while diverging fromforming wire F A couch roll 223 and a turning roll 224 are positioneddownstream of the wire guide 221. Forming wire F is guided aroundturning roll 224 and along the plurality of guide roll 216a back to theupstream portion of the forming system 210. The guide roll 216a may beprovided with tensioning means T substantially as indicated, to maintaina desired degree of tension within the wire run. The first forming wireF carries the newly formed web W along its outer surface and wraps couchroll 223, which is provided with a suction gland 223a to assist inmaintaining the web on the wire F The couch roll 223 directs the formingwire F and the web W away from the forming section and toward a pick-upstation. In the arrangement here shown, the pick-up station is definedby a roll 225 which is wrapped by a pick-up felt PF. Roll 225 isprovided with a suction gland 225a which is maintained undersubatmospheric pressure. The pick-up felt PF contacts the newly formedweb at it travels past the roll 225 and the web W adheres to the pick-upfelt and travel therewith toward a further station for processing asdesired. The pick-up felt PF is, of course, trained around a pluralityof guide rolls (not shown) defining its looped path of travel in aconventional manner. The forming wire F continues to travel upwardlypast the plurality of guide rolls 215a directing the wire F back to theupstream portion of forming system 210. Guide rolls 215a may be providedwith tensioning means T substantially as indicated to maintain thedesired degree of tension within the wire run.

The guide rolls 215a and 216a are also provided with a doctor blade21512 and 21617 respectively, on their offrunning side to cleanse theperipheral surfaces thereof. The doctor blades 215b, 216b direct anyremoved foreign materials, water droplets, etc. into a save-all device217. Suitable drive means M and M are connected to certain of the rollswithin the wire runs F and F In the embodiment here shown, rolls 223 and224 are respectively connected to drive means M and M however, otherrolls may also be connected to such drive means as desired. The drivemeans urge the respective wire runs at speeds substantially equal to thejet-stream speeds, however, they may be regulated to drive the wire atother speeds for certain special effects.

Referring now to FIG. 6 wherein a further modification of thisembodiment of the invention is illustrated. A forming system or section320 is comprised of a head box means 311 having a slice chamber 311aorientated to have its outlet 311e directed in an upward direction. Theslice chamber 311a is likewise provided with a plurality of flexibletrailing members 311b arranged to define a plurality of convergingchannels 313 extending from the head box toward the outlet opening 311e.The converging trailing members 311b have a degree of flexibilityallowing them to assume hydrodynamic stability within the stock flow. Bypositioning the entire head box means 311 upwardly, the bottom apronmember 311a of the head box means need not be curved and the opening311:: can be positioned much closer to the forming gap G.

The arrangement of the various elements in the forming section 320 isquite similar to that described in conjunction with FIG. 6 and they aredesignated by the same reference numeral in the 300 series. Thus, a pairof breast rolls 315 and 316 are mounted for rotation along a generallycommon plane spaced apart a distance to define a somewhatvertically-extending gap G therebetween. The gap G is in close workingrelation with the slice opening 3112 to receive the jet-stream of webstock therefrom. The rolls 315 and 216 are wrapped by forming wires Fand F respectively and guide such forming wires through an initiallyclose spacing at the gap G. The forming wire F is a substantiallycontinuous looped traveling wire having a path of travel defined by aplurality of wire guides 315, 318, 319, 321, 323 and finally 315a so asto constitute a first wire run, for convenience also designated F Thesecond forming wire F is similarly a looped traveling forming wirehaving a path of travel defined by a plurality of wire guides 316, 3-18,319, 321, 324 and 316a so as to constitute a second 'wire run, forconvenience designated F Wire guides 315a and 316a are provided withtensioning means T and T for maintaining a desired degree of tensionwithin their respective wire runs. The paper stock discharges as alow-turbulence, high-dispersion and jet-stream toward the forming gap Gso as to come into contact with the porous surfaces of the forming wireF and P In a preferred embodiment, the jet-stream does not contact thewires until the wires are well beyond the area of pumping influencerolls 315 and 316. Of course, in arrangements where rolls 315 and 316are open rolls pumping is avoided without use of such expediency. Ingeneral, the speed of the jet-stream is sufiicient to cause the water tobe driven through the exposed surfaces of the forming wires at theoff-running side of the breast rolls 315 and 316 by a drainagephenomenon, without disruptive pumping taking place. In this manner, afirst dewatering area A occurs through forming wire F and a seconddewatering area A occurs through the forming wire F so thatsubstantially equal drainage takes place along opposed sides of thenewly forming web. The traveling wires continue to converge togetherinto general parallelism as they travel toward wire guide 318 and wrap aportion of its surface. The wires actually tend to assume generalparallelism at a point 318a along the surface of guide element 318 sothat a gradual buildup of pressure occurs throughout the area ofconvergence. As the wires continue converging together, the exposed sideof forming wire F is free from contact with any detrimental restrainingmeans, thereby defining a third dewatering area A wherein water isdriven through and away from the exposed side of the forming wire FSkimming means and the like can be positioned along this portion of theforming wire run F (along with appropriate save-all devices) to insurethat overloading of this dewatering area does not occur.

The wire guide element 318 is substantially a stationary, smooth,generally convexly curved surface having a relatively large radius ofcurvature. The large radius of curvature prevents any substantiallyloading of the wires against the surface of guide element 318 so thatrelatively little frictional engagement takes place betwen thestationary surface and the traveling wire runs. A large diameterdewatering roll 319 is positioned in close-running relationship with theoff-running side of the guide element 318 so as to provide anessentially continuous path of travel for the sandwich arrangement ofthe traveling wires and the newly forming web. The dewatering roll 319*is here shown as having an open or foraminous structure 319a, whereinthe inner peripheral surface of roll 319 is provided with a plurality ofpins or support structures carrying an outer water-permeable wire meshor the like of conventional construction. Of course other dewateringrolls, such as suction rolls, grooved rolls, drilled rolls, etc. canalso be utilized. The rotating surface of roll 319 offers essentially nofrictional drag on the traveling wires and directs the sandwicharrangement through a rather abrupt curve in relation to the jet-streamdirection at the forming gap G. The abrupt change of direction causesadditional Water to be removed from the sandwich arrangement at afurther dewatering area A Of course, water is also driven in an opposingdirection into openings 319a of roll 319. A save-all device 317 ispositioned in the vicinity of the various dewatering areas to receivethe express water for collecting the same and delivering it via aconduit C back to the head box for dilution of stock or to anotherlocation as desired. A laterally continuous dewatering means 31% and adoctor means 31Gb are operatively associated with save-all device 317for directing any matter coming in contact therewith into such save-alldevice. The dewatering means 31% may be of any structure desired,however, preferably it is an air foil means such as shown and claimed inU.S. Pat. No. 3,377,236 generally comprising a stationary dewateringelement having a rounded lead edge which engages water carried along theexposed surface of the forming wire F without causing anywire-directional-changing engagement with the traveling wires. Thesandwich arrangement continues traveling in a downward direction past astationary dewatering guide 321, 321a substantially as earlierdescribed. The wires F and F then diverge from one another with thenewly formed web W adhering to the wire F for travel therewith around acouch roll 323 having suction gland 323a. Wire F travels around turningroll 324 and back to the forming gap G. The forming wire F and the newlyformed web W travel away from the forming section 320 and toward apick-up station or the like substantially as explained in conjunctionwith FIG. 1. In certain embodiments of the invention. It may bepreferable to position the turning roll 324 substantially below and tothe right of couch roll 323- so that both wires wrap the couch rollduring this area of direction change to insure that the newly formed webdoes not disintegrate or otherwise become disrupted as it is beingguided away from the forming section. This type of couch-turning rollarrangement is further illustrated at FIG. 8.

Referring now to FIG. 7 wherein a somewhat modified web forming section430 is partially illustrated. Various elements shown in forming section430 corresponding to elements discussed in conjunction with FIGS. 5and/or 6 carry the same reference numeral in the 400 series. Thus, ahead box means 411 is positioned in working relation to a forming gap G.A pair of breast rolls 415 and 416 are mounted to rotation in asubstantially vertical plane, each within the loop of one of the formingwires F and F substantially as set forth. It will be noted that the headbox means outlet 411e is orientated generally upwardly to feed thejet-stream of co-moving fibers into contact first with the upper wire,i.e. F and then with the other wire. This orientation allows substantialamounts of water to be driven through such upper wires. After thedewatering areas A A the wires continue traveling convergingly togetherinto general parallelism over a curved wire guide 428 to attain suchparallelism (which has heretofore been defined as a dynamic relationundergoing slight geometric changes as water is removed from the newlyforming web) at a point 428a along the surface of the guide element 428.Respective forming wires F and F are trained over a plurality of wireguides as indicated herebefore to define first and second wire runswhich are driven by substantially jet stream speeds and maintained undertension as desired. As the wires converge together with the stocktherebetween, a first dewatering area A; occurs at the offrunning sideof breast roll 415 and a second dewatering area A occurs at theoff-running side of the breast roll 416.'As the wires travel in generalparallelism substantially greater pressure is gradually applied on thejetstream and additional dewatering takes'place along a third dewateringarea A through the exposed side of the forming wire F which is free fromcontact with any detrimental restraining means. The initial dewateringarea A and A apply easy pressure on the stock between the wires which isdefined for purposes of the invention as a compromise between abruptpressure necessary to expel water from a web and slowly increasing orintensified pressure that avoids spreadin or spewing of the paper stockbeyond the wires.

The guide element 428 presents a substantially waterpermeable surface tothe second wire run F and is defined by a plurality of longitudinallyspaced generally transverse wire-contacting relatively thin edges 42811.The longitudinal contour of the wire-contacting edges 428k define theelongated convex curve of the wire guide 428. The relatively largeradius of curvature of the guiding surface of guide element 428 preventssubstantial normal or perpendicular pressure loading of the wiresagainst the edges 428b thereby preventing undue frictional engagementbetween the traveling wires and the guide surface of the element 428. Incertain embodiments, the guide element 428 includes a housing 4280 alongwith an associated pump means 428d operationally connected therewith formaintaining of subatmospheric pressure at the water-permeable surface soas to aid water removal through the longitudinal spacing between thewire-contacting edges 42%. The conduit C is provided within the housing4280 for directing collected water away to another location. Thus, thewater-permeable surface of element 428 defines a fifth dewatering area Asubstantially opposed to the third dewatering area A While guide element428 preferably has a convexly curved surface, it will nevertheless beappreciated that an essentially flat surface (having an essentiallyinfinite radius) may also be utilized. The arrangement shown at FIG. 7is especially useful for continuously dewatering a newly forming webalong substantially opposed sides thereof thereby providing properdistribution of fibers within the web.

The sandwich arrangement continues traveling in the jet-stream directionso as to contact the portion of the surface of a relatively largediameter foraminous roll 419. Roll 419 is here shown as having an opensurface 419a, however, other dewatering surfaces are also useful. Theroll 419 presents a rotating surface to the traveling sandwicharrangement guiding the same through a substantial curve away from thejet-stream direction at a rate of turn sufificient to centrifugallydewater the sandwiched web and define a fourth dewatering area A drivingwater through and away from the exposed side of the first forming wire FOf course, some water is also dewatered by the surface 419a of the roll419. The roll 419 and guide element 428 cooperate to guide the wiresthrough a continous bi-radii path of travel substantially as describedearlier. The forming wires then continue traveling to an appropriatepick-up station, for example as discussed in conjunction with FIG. 6.

Referring now to FIG. 8, a forming section 510 is generally illustratedshowing an arrangement somewhat similar to that discussed at FIG. 3 andincluding additional modifications, such as discusses at FIG. 6. Apreferred head box means 511 is provided with an essentially symmetricalslice chamber 511a which includes trailing flexible members 512 defininga plurality of converging channels 513 therebetween allowing passage ofstock toward an outlet 5115:. A power adjustment means HP is operativelyconnected with the head box means 511 for orienting the slice chamberand outlet as desired. Continuously looped forming wires F and F arearranged to converge with one another at a gap G. Breast rolls 515 and516 are each mounted within the loop of one of the wires in the mannerdescribed. The rolls 51S and 516 are provided with plural directionadjustment means Ra, as schematically indicated by the four-headedarrows, allowing selective adjustment of the gap dimension as desired.In the arrangement shown, roll 515 is shown as being an open breastroll, while roll 516 is shown as being a solid breast roll, however,both rolls could be solid or open as desired. The upward orientation ofthe slice outlet 5112 and the gap G provides a more compact formingsystem wherein gravity assists in forming desired webs. Further, anyexcess stock or the like will fall down and away from the formingsection and not interfere with the proper web formation. The wires arerespectively trained over a plurality of guide elements 517 and 519 andthen respectively over guides 515a and 516a so as to define first andsecond wire runs similar to those described earlier. The stock isimpinged onto the surface of the forming wires F and F so that water isremoved therefrom by an essentially drainage phenomena without anypumping or the like by the rolls that may cause streaking of the newlyforming web. The dewatering, as indicated at a first area A and a secondarea A is in substantially opposing direction so that simultaneousdrainage, without pumping takes place along both surfaces of the newlyweb for proper fiber distribution within the web, yielding optimumstrength, printing and the like characteristics. The forming wirescontinue to travel together convergingly into general parallelism overthe guide element 517. The guide element 517 is essentially an elongatedsmooth stationary generally convexly curved surface urging wire F intogeneral parallelism with wire F while having stock sandwichedtherebetween. The guide element 517 is here shown as being essentiallywater-impermable, however, it will be appreciated that some slightamount of water as a film, will form on its working surface to act as alubricant for the traveling wire run. Further, as discussed inconjunction with FIG. 7, a water-permeable surface can also be utilized.The generally elongated curvature of the guide element 517 is beneficialin allowing a gradual build-up of pressure between the forming wires andavoids spewing of large volumes of water from between the wires causingflow disturbances due to relatively abrupt and/or intensified changesbetween such wires. As already discussed, the curvature of guide element517 avoids wear of the wire or of the guide element and is lessexpensive than providing a rotating surface having a similar radius ofcurvature.

The wires F and F do not come into actual paralleism with one anotheruntil a point 517a well beyond the lead edge of the guide element 517.The point of convergence 517a is actually adjustable by selectivepositioning of the breast rolls 515 and 516 via their respectiveadjustment means Ra as explained hereinbefore. This adjustment isnecessary to allow the formation of various grades of webs, i.e. whentissue paper webs are being produced, the point of convergence will besubstantially closer to the lead edge of the guide element 517 thanwhen, for example, newspaper grade paper webs are being produced. Duringthis area of gradual convergence of the wires into general parallelismwith one another, additional pressure is gradually applied upon thenewly forming web so that water is thrown through and away from theexposed side of the forming Wire F in the manner shown, to define athird dewatering area A The expressed water (such as at areas A A etc.)is collected in an appropriate saveall device Sa, having a conduit Cdirecting the expressed water back to a desired location. Similardevices are provided beneath the various areas where water is removedfrom the sandwiched forming web.

The utilization of an open breast roll and a stationary curved guideelement in the initial stage of the forming zone provides a positivemeans of water movement control in this critical area of web formationand additionally provides increased drainage capacity with attending lowdrainage pressure which are very important for proper web formation. Aflexible control is provided by the ability to adjust the clearancebetween the two traveling wire runs at the open roll location (i.e. atthe forming gap G), control of the drainage capacities is presented byvirtue of the increased length over which the traveling wires convergeinto general parallelism, while the low drainage pressure is primarilycontrolled via the relatively large radius of curvature of the guideelement 517.

The large diameter suction roll 519 is positioned downstream of theguide element 517, preferably in close running relationship so as todefine a continuous bi-radii path of travel having a first radius ofcurvature substantially larger than the second radius of curvature. Aswill be appreciated, the guide element 517 defines such first radius ofcurvature while the guide element 519 defines such second radius ofcurvature. The suction roll 519 is shown as a large diameter suctionroll having a plurality of vacuum or subatmospheric chambers 519a, 5191:and 51%, each operatively associated with a means 519x, such as pumpmeans P schematically illustrated, for providing a select amount ofsubatmospheric pressure to each of the chambers. The vacuum pressure ineach of the chambers 519a, 51911 and 5190 are of varying strength andare preferably progressively of greater strength, i.e. of increasedvacuum, than the preceding chamber in the direction of wire travel.Thus, for example, chamber 519a is weaker than chamber 51% which in turnis weaker than 519a. As shown, the suction roll 519 receives thetraveling sandwich arrangement of wire-web-wire and directs it through acurve away from the direction of the jet-stream at the slice opening511e. Since the surface of roll 519 is rotating, substantially littlefrictional force is developed between the surface of the roll and thetraveling wires so that no detrimental effects are encountered by virtueof the increased loading on the wires. The rate of turn through whichthe traveling wires are forced by surface of the roll 519 is sufficientto cause dewatering to occur by centrifugal forces driving water throughand away from the exposed side of the forming wire F Of course, water isalso driven and retained within the individual chambers of the suctionroll 519 so as to define additional dewatering areas A A and A The roll519 is driven (as by drive means M at substantially the jet-stream speedof the stock and of the traveling wires so that there is little relativemovement between the traveling wire runs and the supporting surface ofthe roll 519. At the initial wrap of the traveling wires over roll 519,the chamber 519a provides a controlled amount of vacuum against theinner peripheral surface of forming wire F drawing substantial amountsof Water into the dewatering area A This area is of relative small size,i.e., having an arc length of about 20, since in this initial area ofwrap the traveling wires are first guided away from the jet-streamdirection and a substantial amount of centrifugal force will be producedon the traveling sandwich arrangement so that substantial amounts ofwater will be thrown away from this traveling structure and excessivevacuum at this area could be detrimental. The next subatmosphericcompartments 51% is substantially larger in size and has a higher degreeof vacuum thereby drawing additional amounts of water into thedewatering area A as shown. The arc length of compartment 51% may beabout 60", which corresponds to a length of about 63 inches and would becomparable to about five or so suction boxes having a 12 inch length(conventional suction boxes). During this portion of the forming zonedewatering continues to take place upwardly through the forming wire F;with the aid of centrifugal forces and wire tension and downwardly byvirtue of gravity and subatmospheric pressure. The final compartment5190 generally compares to the vacuum length and drainage capacityavailable over a conventional suction couch roll and draws additionalamounts of water into the dewatering area A as indicated.

As will be appreciated, greater amounts of vacuum can be applied insuction rolls than in conventional vacuum flat boxes due to less wirewear, less chance of seizure, etc. Thus, it will be noted that theinstant forming arrangement completely does away with the necessity ofutilizing stationary suction boxes, such as shown in the arrangements ofFIGS. 5-7 and thereby decreases the dimensions of the forming sectionwhile substantially increasing the water handling capacity thereof.Additionally, it will be appreciated that the area of Wire wrap aroundsuction 519 may be adjusted so as to obtain more wire wrap therebyobtaining additional dewatering as desired. Of course, less wrap mayalso be utilized for forming light weight webs.

The further advantage of this arrangement is that roll 519 herefunctions as a couch roll so that the newly formed web W adheres to thelower wire F and departs from the upper wire F The upper wire F isguided by a turning roll 515a and directed back towards a forming gap Gwhile the forming wire F continues to travel along an essentiallystraight line to a pick-up station generally indicated at PN havingelements substantially similar to those previously described. Laterallycontinuous dewatering means 520 and 520a are each respectively trainedon the exposed inner peripheral surface of the forming wires F and F soas to skim off any water that may be adherent to the backside of theforming wire runs. The dewatering means engage and remove the water onthe backside of the wire runs without causing any wire-directionalchangeand there is little, if any, frictional engagement between the travelingwires and the dewatering means 520 and 520a.

The forming system 510 allows the combination of centrifugal forces,gravity and vacuum to effect substantial amounts of dewatering in arelatively short space so that a very compact forming section isprovided. As indicated hereinbefore, the roll 519 is driven by asuitable drive means M and thereby reducing the load or tension on theforming wire F and insure a longer useful life for the wire and lessdisturbances on the sandwich Web. The drive requirements of the otherforming wire, F are also very low since there is no surface causing aheavy drag on this wire. Of course, wire F is shown as being driven bysecond suitable drive means M which is synchronized with drive means Mso that both wires travel at substantially the jet-stream speed over thevarious guides and there is little relative movement between the 'twowires thereby avoiding scutfing or the like of the web that issandwiched between such wires.

It will be noted that suction roll 519 functions as a couch roll in thatit positions the newly formed web W for removal from the forming section510-. As the traveling wires F and F pass over the last subatmosphericcompartments 5190 of the roll 519, they quickly diverge from one anotherand the newly formed web W adheres to the Wire in contact with the couchroll, i.e. P In forming arrangements where a change of travel directionoccurs at a couch roll, it is important to insure that the newly formedweb does not depart from the couch roll but remains in contact with theWire contacting said couch roll for guidance to a pick-up station. Inthe arrangement shown, both wires wrap the couch roll 519 for asubstantial portion of its peripheral surfacethereby preventing thenewly formed web from deviating from the desired path of travel. Wireturning roll 515a controls the amount of wire wrap by wire F over thecouch roll 519. In certain arrangements, wire turning roll 515a isprovided with a plural direction adjustment means, schematicallyindicated at Ra, allowing selective positioning of the roll 515a inrespect to roll 519. It is important to position the roll 515a at alocation insuring that the upper wire F at least wraps that portion ofthe couch roll 519 wherein the greatest amount of direction changeoccurs.

An additional advantage of the arrangement shown is that if the web Wshould, for some reason break after passing beyond the protectivesandwich arrangement, it will naturally fall downwardly into a broke-pitor the like and not otherwise interfere with the remaining web beingproduced.

The forming wire F carries the newly formed web W along its outersurface along an essentially straight line of travel to a pick-upstation PN. An exemplary pick-up station is here illustrated ascomprised of a pick-up felt PF which is trained over a plurality ofrolls, of which only roll 522a is shown, to define a conventionalendless loop. A web transfer roll 522 is positioned within the loop ofthe pick-up felt PF and in close running contact with the wire F so asto contact the web W carried by the wire F The transfer roll 522 isprovided with a suction gland 522b, which is maintained undersubatmospheric pressure in a conventional manner and functions as an aidin transferring the newly formed web W from the forming wire to thepick-up felt. The pick-up felt carries a newly formed web for furtherprocessing as desired, i.e. to a first press section or the like.

As described earlier, the wire guide rolls 515a and 516a are positionedwithin the respective loops of the wires of F and F to guide the same inthe continuous loop throughout the forming section 510. These wire guiderolls can be provided with conventional doctor means 515b and 5161)respectively as well as tension means T and T as desired. Suitable drivemeans M and M are connected to certain of the rolls within the wire runsF and F to maintain the speed of the traveling wire runs at a selectedspeed, preferably at substantially the jet-stream speed. In theembodiment here shown, one of the rolls within the loop of wire F i.e.roll 515A and two of the rolls within the loop of wire F i.e. suctionroll 519 and guide roll 516a are the driven rolls, however, otherarrangements also provide satisfactory operation.

Accordingly, the instant forming arrangement provides a path of travelfor a pair of opposed forming wires over a plurality of curved guidesurfaces defining a bi-radii path of travel that substantiallycorresponds to the jetstream trajectory at a slice chamber opening sothat substantial amounts of natural drainage are allowed to take place,augmented by various other forces, i.e. centrifugal forces, gravity,vacuum, etc. to obtain efficient and fast dewatering of a forming weband that there is no second and/r reverse wrap in the path of travel ofthe wires carrying the web therebetween thereby avoiding detrimentalwear of the wires or any possibility of web scufiing or the like. Theforming system of the invention and particularly of the arrangement hereshown, is capable of operations well above 3000 feet per minute for avariety of paper grades and it is extremely compact and easy tomaintain, affording numerous advantages.

In summation, the invention provides a web forming system (preferablyfor use in paper formation) generally comprising a head box means forsupplying a stream of web stock in a given direction, a pair of loopedforming wires arranged to converge and provide an entrance nip for thereception of stock, means for supporting the wires within the respectiveloops and moving them into the entrance nip, curved guide elementspositioned downstream and adjacent the entrance nip, within the loop ofone of the wires so that the wires travel over a portion of the surfacesof the guide elements while having stock there- 22 between at a speed sothat the stock is dewatered at least in part by centrifugal forcesthrough one of the wires.

A specific preferred form of head box means comprises a stock supplymeans and a slice chamber means positioned in working relation with thesupply means and with respect to the entrance nip of the forming wires.The slice chamber means has an outlet opening, first and second wallsconvering toward the outlet opening and a plurality of flexible trailingelements within the slice chamber arranged to define therebetweenconverging channels extending toward the outlet opening for guiding adilute aqueous stock suspension therethrough as a suspension ofentrangled co-moving fibers having a relatively low degree of turbulenceand a relatively high degree of dispersion in a high speed, ribbon thin,substantially unidirectional, jet-like stream toward the outlet opening.

A specific preferred form of the curved guide elements comprises astationary curved surface positioned adjacent the entrance nip and arotary cylinder positioned downstream of the stationary surface so as todefine therewith a continuous bi-radii curved path of wire travel havingthe first radius of curvature substantially larger than a second radiusof curvature so that initially relatively gentle pressure is exerted onthe stock between the wires and thereafter increased amounts of pressureare exerted on the stock. The stationary surface and rotating cylinderare arranged on the same side of the wires and have water-permeable orwater-impermeable constructions. Also, the stationary curved surface hasa relatively large radius of curvature, which is constant or decreasingin the direction of wire travel. In certain arrangements the rotarycylinder is provided with suction glands and functions as a couch rollin transferring the newly formed web away from the forming system.

The drawings and the specification present a detailed disclosure of thepreferred embodiments mentioned and it is to be understood that theinvention is not limited to the specific forms disclosed. Accordingly,it will be understood that modifications and variations may be effectedwithout departing from the spirit and scope of the novel concepts of thepresent invention.

We claim as our invention:

1. An apparatus for forming fibrous webs comprising:

first and second continuous looped foraminous forming wires which arearranged to converge and provide an entrance nip for the reception ofweb-forming stock;

a curved stationary surface positioned adjacent said entrance nip; meansfor supporting said wires within their respective loops and moving saidwires into said entrance nip;

said forming wires being arranged to travel over said stationary curvedsurface downstream of said entrance nip while having stock therebetween,

a rotary cylinder,

said wires traveling around a part of the periphery of said rotarycylinder immediately following the stationary forming surface, with saidsurface and said cylinder being on the same side of said wires;

said stationary curved surface having a relatively large radius ofcurvature;

the first wire being free of restraining means on its outer surfaceopposite said rotating cylinder;

said wires arranged for traveling at a speed so that the stock isdewatered centrifugally through the first wire.

2. An apparatus as defined in claim 1 wherein the first wire passes overa roll for guiding it into said entrance nip.

3. An apparatus as defined in claim 2 including means for adjusting saidroll relative to the entrance nip.

'4. An apparatus for forming a fibrous web as defined in claim 1 whereinsaid wires wrap a guide roll after leaving the rotary cylinder with thefirst wire engaging said guide roll.

5. An apparatus for forming fibrous webs as defined in claim 4 whereinthe guide roll is a suction roll.

6. An apparatus for forming fibrous webs as defined in claim 4 includingmeans for adjusting said roll relative to the rotary cylinder.

7. An apparatus for forming fibrous Webs as defined in claim 1 includingmeans for separating the first wire from the second wire following therotary cylinder with the web being carried on the second wire.

8. An apparatus for forming fibrous webs as defined in claim 7 includinga web transfer means positioned downstream of the rotary cylinder and inworking relation with the second wire for transferring the web away fromsaid second wire.

9. An apparatus for forming fibrous webs as defined in claim 8 includingmeans forming a second sequence for forming a new ply of web over theweb on the second forming wire comprising a third looped forming wirearranged to provide an entrance nip with the second forming wire afterit has been separated from the first forming wire for the reception ofstock on the surface of the web carried by the second forming wire, acurved stationary surface positioned adjacent said entrance nip, meansfor supporting said second and third wire within their respective loopsand moving said second and third wires into said entrance nip, saidsecond and third wires eing arranged to travel over said stationarycurved surface downstream of said entrance nip while having stocktherebetween, a rotary cylinder, said second and third wires travelingaround a part of the periphery of said rotary cylinder immediatelyfollowing the stationary curved surface, with said stationary surfaceand said rotary cylinder being on the same side of the wires to sup portsaid second wire, said stationary curved surface having a relativelylarge radius of curvature, the third wire being free of restrainingmeans on its outer surface opposite the rotary cylinder, said second andthird wires arranged for traveling at a speed so that the stock isdewatered centrifugally through the third wire.

10. An apparatus for forming a fibrous web comprismg:

first and second continuous looped foraminous forming wires which arearranged to converge and provide an entrance nip for the reception ofweb-forming stock;

a curved stationary surface positioned adjacent said entrance nip;

means for supporting said wires within their respective loops and movingsaid wires into said entrance nip;

said forming wires being arranged to travel over said stationary curvedsurface downstream of said entrance nip while having stock therebetween;

a rotary cylinder positioned downstream in close-working relation withsaid curved stationary surface to define a continuous bi-radii curvedpath of wire travel having a first radius of curvature substantiallylarger than a second radius of curvature;

said wires traveling around a part of the periphery of said rotarycylinder immediately following the stationary curved surface, with saidstationary surface and said rotary cylinder being on the same side ofsaid wires;

the first wire being free of restraining means on its outer surfaceopposite said rotary cylinder;

said wires arranged for traveling at a speed so that the stock isdewatered centrifugally through the first wire.

11. An apparatus for forming fibrous webs as defined in claim 10 whereinthe curved stationary surface is a substantially water-permeable surfacedefined by a plurality of longitudinally spaced generally transversewirecontacting relatively thin edges, the longitudinal contour of saidwire-contacting edges defining the curve of said surface.

12. An apparatus for forming fibrous webs comprising:

first and second continuous looped foraminous forming wires which arearranged to converge and provide an entrance nip for the reception ofweb-forming stock; a curved stationary surface positioned adjacent saidentrance nip; means for supporting said wires within their respectiveloops and moving said wires into said entrance nip; said forming wiresbeing arranged to travel over said stationary curved surface downstreamof said entrance nip while having stock therebetween; a rotary cylinder;said wires traveling around a part of the periphery of said rotarycylinder following the stationary surface with said stationary surfaceand said rotary cylinder being on the same side of said wires; saidcurved surface being a substantial water-permeable surface defined by aplurality of longitudinally spaced generally transverse wire-contactingrelatively thin edges, the longitudinal contour of said wirecontactingedges defining the curve of said waterpermeable surface; The first wirebeing free of restraining means on its outer surface opposite saidrotary cylinder; said wires arranged for traveling at a speed so thatthe stock is dewatered centrifugally through the first wire. 13. Anapparatus for forming a fibrous web as defined in claim 12 wherein thewire-contacting thin edges are connected to a housing and means areconnected to said housing for maintaining a subatmospheric pressure inthe spacing between said wire-contacting thin edges for water removalthrough said spacing.

14. An apparatus for forming fibrous webs comprising, in combination:

first and second continuous looped foraminous forming wires which arearranged to converge and provide an entrance nip for the reception ofweb forming stock;

means for supporting said wires within their respective loops and movingsaid wires into said entrance nip;

a stock supply means and a slice chamber means positioned in workingrelation with said stock supply means and with respect to said entrancenip;

said slice chamber having an outlet opening, a first and second wallconverging toward said outlet opening and a plurality of flexibletrailing elements within said slice chamber arranged to definetherebetween converging channels extending toward said outlet openingand guiding a dilute aqueous stock suspension therethrough as asuspension of entangled comoving fibers having a relatively low degreeof turbulence and a relatively high degree of dispersion in a high-speedribbon-thin substantially unidirectional jet-like stream toward saidoutlet opening:

a curved stationary surface positioned adjacent said entrance nip;

said forming wires being arranged to travel over said stationary curvedsurface downstream of said entrance nip while having stock therebetween;

a rotary cylinder positioned downstream with said curved stationarysurface to define therewith a continuous bi-radii curved path of wiretravel having a first radius of curvature substantially larger than asecond radius of curvature;

said wires traveling around a part of the periphery of said rotarycylinder following the stationary curved surface, with said stationarysurface and said rotary cylinder being on the same side of said wires;

the first wire being free of restraining means on its outer surfaceopposite said rotary cylinder;

said wires arranged for traveling at a speed so that the stock isdewatered centrifugally through the first wire, whereby initiallyrelatively gentle pressure is exerted on the stock between the wires andthereafter increased amounts of pressure are exerted on said stock.

15. An apparatus for forming fibrous webs as defined in claim 14including means for adjusting the outlet opening of the slice chamber inrelation to the entrance mp.

16. An apparatus for forming fibrous webs as defined in claim 14 whereina stationary water-removing surface is positioned downstream of therotary cylinder.

17. An apparatus for forming fibrous webs as defined in claim 14 whereinthe curved stationary surface is defined by a relatively large radius ofcurvature for preventing substantially perpendicular pressure loading bythe forming wires as they travel over said stationary surface.

18. An apparatus for forming fibrous webs as defined in claim 14including means to orientate the slice chamber outlet so as to guideaqueous suspension of co-moving fibers generally upwardly in respect tothe entrance nip whereby the aqueous suspension generally contacts thefirst wire before coming into contact with the second wire.

19. An apparatus for forming fibrous webs as defined in claim 18including a web transfer means positioned downstream of the rotarycylinder in working relation with the second wire for transferring theweb away from said second wire.

20. An apparatus for forming fibrous webs as defined in claim 14 whereinthe rotary cylinder is a dewatering roll.

21. An apparatus for forming fibrous webs as defined in claim 20 whereinthe dewatering roll is a foraminous roll.

22. An apparatus for forming fibrous webs as defined in claim 21 whereinthe foraminous roll is a suction roll.

23. An apparatus for forming fibrous webs as defined in claim 22including means for separating the first wire from the second wirefollowing the rotary cylinder with the web being carried on the secondwire and a web transfer means positioned downstream of the rotarycylinder in working relation with the second wire for transferring theweb away from said second wire.

References Cited S. LEON BASHOR E, Primary Examiner R. H. TUSHIN,Assistant Examiner US. Cl. X.R.

